For the extraction of ore from ore material, freshly supplied ore material must be prepared in several process stages, the first stages of the preparation process including a suitable comminution of the fresh ore material supplied from a mine. For this purpose various methods, apparatus and comminution arrangements are known in the art. For instance, much use has been made recently of so-called material bed comminution in material bed roll mill, in which ore material pre-comminuted in a preceding crusher, e.g. a gyratory crusher or roll crusher, is further comminuted or finely comminuted in the grinding gap between two rolls which are pressed against one another with relatively high pressure and are driven so as to revolve in opposite directions. In this material bed comminution the pre-comminuted ore material is finely comminuted very thoroughly with a relative saving of energy, and the comminuted product coming from this material bed comminution or the corresponding material bed roll mill is obtained at least partially in the form of agglomerates, so-called scabs, which if required can be disagglomerated with the aid of simple equipment. The sufficiently finely comminuted ore material can be be separated off, optionally with the aid of a suitable screening or classifying arrangement, and drawn off as finished material or delivered to the subsequent stage of the preparation process, whilst any ore material which is not sufficiently comminuted is delivered for further comminution.
Brittle materials above all can be comminuted very effectively and with a saving of energy in material bed roll mills. In practical use, however, it has frequently proved to be a disadvantage that the throughput of the material bed roll mill is greatly reduced if the ore material to be comminuted contains components which are particularly fine, plastic, sticky or the like, as is the case for example with argillaceous fresh ore materials.
In other known methods and apparatus so-called autogenous mills are used for the comminution of the fresh ore material which may have been pre-crushed. In this comminution in an autogenous mill a certain proportion of the comminuted material can optionally be recirculated. In this case there are also constructions in which there is arranged after an autogenous mill at least one drum mill or agitator mill in which the comminuted product obtained in the autogenous mill is then reground to the desired fineness of the finished product. These mills can also be interconnected with a classifier so that the ore material is comminuted in a closed circuit and sufficiently fine material is drawn off from the classifier as finished material. An autogenous mill is a type of drum mill of relatively large diameter in which the pieces of material simultaneously form the grinding elements but in which in the case of certain materials a limited proportion of additional grinding elements in the form of grinding balls or the like can be added (in the latter case these are referred to as semi-autogenous mills).
A disadvantage of these autogenous mills described above is that their grinding efficiency is relatively low and therefore very large amounts of energy have to be expended for the comminution work to be carried out. Furthermore, in such an autogenous mill certain materials tend to form critical grain sizes which are only reduced to a small extent and thus by remaining in the mill lead to a considerable reduction in the throughput, often associated with an additionally increased energy consumption. The occurrence of critical grain sizes or grain fractions is in many cases attributable to ore materials consisting of components of differing grindability.
The object of the invention is to create a method of comminution by means of which, even in the case of ore material compositions consisting of differing components and even with undesired fine material fractions, plastic fractions, sticky fractions or the like in the ore material (starting ore material), an optimal comminution of these ore materials can be achieved with a relatively high throughput.